Add test of all:benches

cabal-testsuite/PackageTests/Target/cabal.all-benches.out

@@ -0,0 +1,8 @@
+# cabal clean
+# cabal v2-target
+Configuration is affected by the following files:
+- cabal.project
+Resolving dependencies...
+Fully qualified target forms:
+ - a:bench:a-bench
+ - b:bench:b-bench

cabal-testsuite/PackageTests/Target/cabal.test.hs

@@ -16,3 +16,7 @@ main = do
   cabalTest' "all-tests" $ do
     cabal "clean" []
     cabal "v2-target" ["all:tests"]
+
+  cabalTest' "all-benches" $ do
+    cabal "clean" []
+    cabal "v2-target" ["all:benches"]

cabal-testsuite/PackageTests/Target/dir-a/a.cabal

@@ -9,4 +9,7 @@ library a-sublib
 executable a-exe
 test-suite a-test
     type: exitcode-stdio-1.0
-    main-is: Test.hs
+    main-is: Test.hs
+benchmark a-bench
+    type: exitcode-stdio-1.0
+    main-is: Bench.hs

cabal-testsuite/PackageTests/Target/dir-b/b.cabal

@@ -9,4 +9,7 @@ library b-sublib
 executable b-exe
 test-suite b-test
     type: exitcode-stdio-1.0
-    main-is: Test.hs
+    main-is: Test.hs
+benchmark b-bench
+    type: exitcode-stdio-1.0
+    main-is: Bench.hs